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fix(font): bound CFF indices and dictionary operands - #1058
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A PDF falls back to a substitute font when its embedded font is refused, so the page shows the wrong glyphs. These quirks now pass, as before this change: an INDEX whose first offset is not one, an unreadable real (it reads as zero), a reserved nibble, trailing DICT operands, a charset range past the glyphs (clipped), and FDSelect ranges that are out of order, past the glyphs or name an unknown FD (widths_for_glyph falls back). The bounds of INDEX, DICT and charstring reads stay strict. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Gb1fLafqqzehpqPuU6uBfn
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CFF INDEX iteration could wrap at 65,535 entries, offsets could wrap or point outside the font, and dictionary/glyph reads could consume bytes from the next structure. Bound each view and validate ranges before expansion or integer conversion. Real operands use the shared locale-independent number parser. A quirk that only affects one glyph or operand does not refuse the font: an unreadable real reads as zero, a charset range past the glyphs is clipped, and FDSelect ranges out of order or with an unknown FD fall back to the Top DICT widths.
Validation: all 50 PDF corpus cases pass, alongside the font and Type1 suites. The corpus logs retain a missing-glyph font substitution and cross-reference recovery warning. Four focused regressions cover maximum INDEX counts, invalid ranges/operands, German numeric locale, and FDSelect coverage. Bounds follow Adobe CFF sections 4, 5, 13 and 19.